Extracellular Domain Mutations in EGFR Occur Uniquely in Glioblastoma and Favor Ligand-Independent Formation of the Active State

Susan L. McGovern, Marta L. Rojas, Anupama Gururaj, Wah Chiu, Oliver Bogler, and John N. Weinstein

Departments of Radiation Oncology, Neurosurgery, and BiostatisticsMD Anderson Cancer Center

Department of BiochemistryBaylor College of Medicine

Houston, TX

ASTRO 2012

Cancer

COSMICExtracellular

missense mutations in

EGFR

Intracellularmissense

mutations in EGFR

Lung adenoca 0 2282

Lung SCC 0 38

Lung BAC 0 48

Ovarian 0 18Head & neck 0 19

Mesothelioma 0 9

Prostate 0 29

Thyroid 0 15

Glioblastoma 68 8

Cancer

COSMIC TCGA Validation SetExtracellular

missense mutations in

EGFR

Intracellularmissense

mutations in EGFR

Extracellular missense

mutations in EGFR

Intracellularmissense mutations

in EGFRLung adenoca 0 2282

Lung SCC 0 38

Lung BAC 0 48

Ovarian 0 18Head & neck 0 19

Mesothelioma 0 9

Prostate 0 29

Thyroid 0 15

Glioblastoma 68 8 35 1

Cancer

COSMICExtracellular

missense mutations in

EGFR

Intracellularmissense

mutations in EGFR

Lung adenoca 0 2282

Lung SCC 0 38

Lung BAC 0 48

Ovarian 0 18Head & neck 0 19

Mesothelioma 0 9

Prostate 0 29

Thyroid 0 15

p < 10-100

What is the pattern of missense mutations in EGFR in glioblastoma?

21 missense mutations (A289V/D/T)

14 missense mutations (G598V)

7 missense mutations (R108K)

4 missense mutations (T263P)

2 missense mutations (R324L, P596L, C620W/Y)

1 missense mutation (16 residues)

EGF

Structure of EGFR monomer (1NQL) Structure of EGFR dimer (3NJP)

extracellular

intracellular

III

III

IV

III

III

IV

R108KT263P

A289DA289T

EGFRvIII

EGFR

1726-zeo

Rel

ativ

e P

hosp

hory

latio

n

Y1068 Serum starved

EGF

R108KT263P

A289DA289T

EGFRvIII

EGFR

1726-zeo

Rel

ativ

e P

hosp

hory

latio

n

Y845 Serum starved

EGF

Point mutants show increased phosphorylation in the absence of EGF.

Bogler lab, MDACC

Bogler lab, MDACC

Point mutations have worse survival than wt EGFR.

Point mutants have better survival than EGFR vIII.

XenograftMedian survival (d)

p-value vs. wt EGFR

p-value vs. EGFR vIII

wt EGFR 16 --- 0.0001

EGFR vIII 13 0.0001 ---

R108K 13 0.0017 0.06

T263P 17 0.068 0.0001

A289D 14 0.03 0.0005

A289T 14 0.012 0.0005

Mice transfected with xenografts expressing point mutants or EGFR vIII.

A289T: pulling open latch?A289D: pulling open latch?R108K: loss of hydrogen bondswild type EGFR

A289

R108K

E84A289D

R108

E84A289

R108

E84A289T

R108

E84A289

R108

E84

I

II

III

IV

Model for A289T/D or R108K

Adapted from Li, et al. Cancer Cell (2005)

I

III

IV

III

III

IV

II

IV

EI

II

III

IV

E

III

III

IVI

III

IIIV

A289V or R108K

wt EGFR

95% 5%

EI

III

IV

III

III

IV

II

IV

E

I

III

IIIV

III

III

IV

Conclusions

1. In GBM, EGFR missense mutations preferentially occur in extracellular domain.

2. Many of these mutations may promote ligand-independent activation of EGFR.

3. Better understanding of the biophysical and cellular consequences of these mutations may help identify subgroups of glioblastoma patients that may benefit from EGFR inhibitors (+ other therapies?)